Spectrum Management 2002 Marc Goldburg CTO, Internet Products Group ArrayComm, Inc. Adaptive Antennas (or “doing more with less”)

2 Cellular Technology Coverage area divided into cells Each with infrastructure and users Typical of two-way wireless “cellular” (1G, 2G, 3G, …) MMDS Wireless LANs LMDS Switching/ Routing cell sector Switching/ Routing Data Networks Telephony Networks Backhaul Network base station

3 Spectrum Management Challenges Inter-System management  co-channel at service boundaries  adjacent channel within coverage area Intra-system management  balancing service quality and capacity  self-interference reduces capacity Preview of adaptive antennas  reduce adjacent band emissions  reduce sensitivity to in-band emissions  mitigate in-band interference, increasing capacity  provide gain, increasing range and quality

4 Outline Spectral efficiency Adaptive antenna fundamentals Coexistence

5 Spectral Efficiency Defined Information delivered per unit of spectrum Measured in bits/second/Hertz/cell, includes effects of  multiple access method  modulation methods  channel organization  resource reuse (code, timeslot, carrier, …) “Per-Cell” is critical  primary spectral efficiency limitation generally self-interference  isolated base station results not representative of real-world Spectral Efficiency Interference Management

6 Why Is Spectral Efficiency Important? For given service and grade of service, determines  required amount of spectrum (CapEx)  required number of base stations (CapEx, OpEx)  required number of sites and associated site maintenance (OpEx)  and, ultimately, consumer pricing and affordability Quick calculation (capacity limited system) Affects radiated power per km 2, too number of cells/km 2 = offered load (bits/s/km 2 ) available spectrum (Hz) x spectral efficiency (bits/s/Hz/cell)

7 Designing For Spectral Efficiency Spectral/Temporal tools  multiple access method and data compression optimize efficiency based on traffic characteristics  modulation, channel coding, equalization optimize efficiency based on link quality Spatial tools, interference management  cellularization mitigate co-channel interference by separating co-channel users  sectorization mitigate co-channel interference through static directivity  power control use minimum power necessary for successful communications

8 Self-Interference and Capacity cells sectors serving sector user interference sectorized cells sectors serving sector user interference adaptive antennas

9 Outline Spectral efficiency Adaptive antenna fundamentals Coexistence issues

10 Adaptive Antennas Defined Systems comprising  multiple antenna elements (antenna arrays)  coherent processing  processing strategies that adapt to environment Providing  gain and interference mitigation  improved signal quality and spectral efficiency  improved coexistence behavior

11 Adaptive Antenna Concept +1 2bs 2 (t) +1 2as 1 (t) as 1 (t)+bs 2 (t) as 1 (t)-bs 2 (t) User 2, s 2 (t)e j  t Users’ signals arrive with different relative phases and amplitudes Processing provides gain and interference mitigation User 1, s 1 (t)e j  t as 1 (t)

12 In-Band Uplink Gain Signal s, M antennas, M receivers with i.i.d. noises n i Adaptive antennas improve uplink SNR by factor of M M=10, 10x SNR improvement, examples  double data rate if single antenna SNR is 10 dB  reduce required subscriber transmit power by 10 dB  increase range by 93% with R 3.5 loss s sreceived signal noisen 1 + … + n M = therefore, Uplink SNR (Ms) 2 M2M2 s2s2 22 M== = M x single antenna SNR

13 Similar to uplink calculation,  except dominant noise is due to (single) receiver at user terminal With same total radiated power P in both cases Adaptive antennas improve downlink EIRP by factor of M M=10, 10 dB gain examples  10 elements with 1 W PA’s, same EIRP as single element with 100 W PA  90% reduction in total radiated power for same EIRP In-Band Downlink Gain EIRP (Adaptive Antenna) EIRP (Single Antenna) = (  P/M s + … +  P/M s) 2 (  Ps) 2 = M

14 Out-of-band gain different from in-band gain  non-linearities that create out-of-bands destroy coherency With same total in-band radiated power P in both cases Ratio of in-band:out-of-band gains approximately M  very different from conventional systems M=10, 10 dB gain examples  out-of-band gain up to 90% less than in-band gain Out-of-Band Downlink Gain In-band gain (Adaptive Antenna) Out-of-band gain (Adaptive Antenna)  M(  P/M s) 2 = M (M  P/M s) 2

15 In-Band Interference Mitigation Directive gain results in passive interference mitigation Active interference mitigation additive (in dB) to gain Gain and interference mitigation statistical quantities  Theoretical gain closely approached (within 1 dB) in practice  Theoretical interference mitigation, , harder to achieve limited by calibration, environment, scenario active mitigation in excess of 20 dB can be reliably achieved

16 Processing Gain Operational Significance Selective Uplink GainIncreased Range & Coverage Increased Data Rates Reduced System – Wide Uplink Noise Improved Uplink Multipath Immunity Improved Signal Quality Maintained Quality with Tightened Reuse Increased Range & Coverage Increased Data Rates Reduced System–Wide Downlink Interference Improved Co–existence Behavior Reduced Downlink Multipath Maintained Quality with Tightened Reuse Uplink Interference Mitigation Selective Downlink Gain Downlink Interference Mitigation In-Band Benefits Actual level of benefits depends on implementation details

17 Antenna Arrays Wide variety of geometries and element types  arrangements of off-the-shelf single elements  custom arrays Array size  vertical extent determined by element gain/pattern as usual  horizontal extent, typically 3-5 lambda 2 GHz, eight 10 dBi element array is 0.5 x 0.75 m  small!  conformal arrays for aesthetics

18 Outline Spectral efficiency Adaptive antenna fundamentals Coexistence issues

19 Co-Channel Coexistence Adaptive antennas (AA’s) reduce in-band emissions  factor of M less total radiated power for same EIRP  peak interference remains the same  average interference significantly improved  RF safety/exposure benefits AA’s less sensitive to in-band interference  active interference mitigation can “null” interferers  reduced planning (frequency, separation) requirements

20 Adjacent Channel Coexistence AA out-of-bands have reduced directionality  generating non-linearities destroy element-to-element coherence  lack of coherence reduces directionality  out-of-band gain roughly a factor of M less than in-band gain  peak out-of-band gain closer to average out-of-band gain AA’s less sensitive to out-of-band interference  active interference mitigation can “null” interferers  reduced planning (frequency, separation) requirements

21 Summary Adaptive antennas lead to  increased spectral efficiency, better use of spectrum  affordable, diverse services  improved coexistence behavior Adaptive antennas are becoming pervasive  more than 100,000 deployments worldwide  as a backwards compatible upgrade to existing networks  as a fundamental element of new broadband networks